1. Field of the Invention
The present invention relates to detection of proximity of certain objects to others in general, and more particularly to methods and arrangements for detecting the proximity of stationary obstacles to moving motor vehicles.
2. Description of the Related Art
There are already known various constructions of arrangements for detecting the proximity of one object to another, among them such that detect the distance between a moving object, especially a motor vehicle, and a stationary object or obstacle, and issue a warning when the two get too close together. Arrangements of the latter type and methods performed by them are typically employed in parking aid systems, such as one developed by the assignee of the present invention and known under the designation Parkpilot. The system of this kind includes a plurality of sensors that are located on the vehicle in question and that serve both to transmit signal pulses and receive echoes of such transmitted signal pulses that have been reflected by any obstacle that may be present within the effective ranges of such sensors.
Each such echo can be received either by the sensor at which the original signal pulse had originated, or by any neighboring sensors. The above-mentioned system detects the presence of an obstacle on the basis of the respective echo and generates various warning signals, among them a stop signal that advises the driver of the vehicle to bring the vehicle to an immediate halt, or when the time interval elapsing between the issuance of the signal pulse and the arrival of the echo of such pulse at any neighboring sensor is below a second threshold. The first threshold defines a part-circular region around the sensor as considered in cross section, the detection of presence of any object within which will lead to the generation of the stop signal. The second threshold defines a part-elliptical region as considered in cross section with focal points located at the respective signal transmitter and signal receiver in question, and the detection of presence of any object in this region will also trigger the generation of the stop signal. The magnitudes of the first and second thresholds are chosen in such a manner that the overlap of the part-circular and/or part-elliptical regions will form a strip or band having as constant a width as possible or feasible as measured from a baseline on which the sensors are located.
The substantially uniform width of the strip is important in order to accomplish uniform reliability of the warning during the approach of the obstacle over the entire length of the baseline, and to prevent the possibility that small objects or obstacle could get unnoticed into the vicinity of or even into contact with the part of the vehicle over which the sensors are distributed. On the other hand, for cost reasons, it is desirable to keep the number of the sensors as low as possible; yet, the greater the distance of the sensors from each other relative to the width of the strip, the more pronouncedly the width fluctuates over the course of the baseline.
This problem is especially aggravated when, for instance, sensors with a limited aperture angle are being used, and/or when the distance between the individual sensors cannot be made constant because of external boundary conditions.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a method of detecting the presence of an object, such as an obstacle, in the proximity of another of another object, such as motor vehicle bumper, which method would not possess the drawbacks of the known methods of this type.
Still another object of the present invention is to devise a method of the type here under consideration which would make it possible to maintain the width of a region within the presence of an obstacle will be detected substantially uniform even if the spacing between the sensors is not.
It is yet another object of the present invention to design an arrangement for performing the above method the above in such a manner as to be alerted to the presence of smaller obstacles no later than that of larger obstacles.
A concomitant object of the present invention is so to construct the arrangement of the above type as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.
In keeping with the above objects and others which will become apparent hereafter, one feature of the present invention resides in a method of detecting the presence of an obstacle in the vicinity of an object. This method includes emitting a pulsed signal from a predetermined location of the object, receiving echoes of such a pulsed signal as reflected from the obstacle at at least two locations of the object, measuring respective time intervals elapsing between the emitting and receiving steps, and establishing the presence of the obstacle in a first environmental region of the object when at least one of the time interval to a first one of the two locations is smaller than a first threshold and the time interval to a second one of the two locations is smaller than a second threshold. The method of the present invention further involves the steps of selecting a third and a fourth threshold to exceed by predetermined amounts the first and second threshold, respectively, and establishing the presence of the obstacle in a second environmental region of the object when the time interval to the first location is smaller than the third threshold and the time interval to the second location is simultaneously greater than the fourth threshold. Advantageously, there may further be employed the step of establishing the presence of the obstacle in another second environmental region of the object when the time interval to the second location is smaller than the third threshold and the time interval to the first location is simultaneously greater than the fourth threshold.
The present invention is also directed to an arrangement for detecting the presence of an obstacle in the vicinity of an object, this arrangement comprising means for emitting a pulsed signal from a predetermined location of the object, means for receiving echoes of such a pulsed signal as reflected from the obstacle at least two locations of the object, and means for evaluating the echoes, including means for measuring respective time intervals elapsing between the emission of the pulsed signal by the emitting means and the receipt of the respective echoes by the receiving means, and means for establishing the presence of the obstacle in a first environmental region of the object when at least one of the time interval to a first one of the two locations is smaller than a first threshold and the time interval to a second one of the two locations is smaller than a second threshold, and the presence of the obstacle in a second environmental region of the object when the time interval to the first location is smaller than a third threshold exceeding the first threshold and the time interval to the second location is simultaneously greater than a fourth threshold exceeding the second threshold.
A particular advantage of the method and arrangement of the present invention as described so far is that they render it possible selectively to widen the strip from the boundary of the object within which the presence of an object is detected at a location that previously was particularly vulnerable to undetected passage therethough especially of relatively small obstacles, without increasing the width of the strip at other locations at which the width of the strip is sufficient for providing early enough warning of the presence of obstructions large and small, which would be the result if the magnitudes of the first and second thresholds were to be increased. The above method and arrangement is particularly useful when employed on or embodied in motor vehicles, especially their rear bumpers.
According to an advantageous facet of the present invention, the receiving means includes first and second receivers situated at the first and second locations of the object, respectively, and wherein the second environmental region is situated in its entirety at a side of the second receiver that is remote from the one receiver and at a predetermined distance from a plane normal to an imaginary line connecting the first and second receiver and passing through the second receiver. This avoids the otherwise exiting possibility of premature triggering of the alarm especially by large obstacles.
To achieve a simpler construction of the arrangement of the present invention, the receiving means includes substantially identical first and second receivers situated at the first and second locations of the object, respectively, and each simultaneously capable of serving as the emitting means. Such transmitters/receivers or transceivers then constitute simply sensors that are interchangeable with one another during the assembly of the arrangement and, moreover, can be produced less expensively than dedicated devices.
In order to be able to achieve reliability in the detection of obstacles in the vicinity of the object in question, it is proposed in accordance with the present invention that the receiving means include at least two pairs of receivers distributed along a border line of the object. When the object is a motor vehicle, then the border line is advantageously situated at the outer surface, and extends along the length, of a bumper of the motor vehicle.
It is especially advantageous for the receivers of the respective pair to be separated from each other by a distance smaller than that between any of the receivers of different ones of the pairs.
Last but not least, advantageous results especially as far as obstacle detection coverage is concerned is achieved when, in accordance with another aspect of the present invention, the third and fourth thresholds are chosen in such a manner that the second environmental regions of the two pairs of sensor overlap each other beyond the first environmental region.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.